Figure 17.21. Invasive ductal carcinoma of no special type (x250).

cases). Histologically, the tumour cells can be arranged in groups, cords and can also form gland-like structures set in a dense fibrous stroma, which gives the tumour a hard consistency (scirrhous tumour) (Fig. 17.21).

The degree of aggressiveness of these tumours is variable and can be determined from the cytological and histological appearances of the tumour cells. Bloom and Richardson developed a grading system (1-3) for these tumours which was based on three characteristics: (i) the formation of tubules; (ii) the degree of nuclear pleomorphism and (iii) the mitotic rate. Grade 3 tumours have the worst prognosis, with grade 1 tumours having the best outcome.

Invasive lobular carcinoma

Invasive lobular carcinoma occurs much less frequently, comprising less than 5% of all breast cancers. Histologically, there are strands of tumour cells which infiltrate into the surrounding stromal tissues; typically these are one cell in width ('Indian filing'). Tumour cells may also be found in concentric rings around normal ducts (Fig. 17.22). However, in some cases it can be difficult to differentiate between an invasive ductal and an invasive lobular cancer. Furthermore, both of these types may co-exist in the same tumour. This tumour can be multicentric within the same breast and is bilateral in up to 20% of patients.

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